Bodily training is of little benefit, he says, however, godliness contains the promise of this and the future life. By bodily training, some understand the training of the body, as when one trains and is motivated to maintain bodily health and increase bodily strength. Others take it to mean practice of the ceremonial Law, which the apostle describes in Heb. 9:13, as bodily cleansing. However, the best explanation can be obtained from the previous words of this fourth chapter. For there the holy apostle proclaims that in the last times, seductive spirits will appear who will teach to abstain from food which God has created to be received with thanksgiving (v. 3). That is to say, they will make the distinctions about food a part of worship, and will forgo godliness—yes, even the grace of God and salvation which they possessed. The holy apostle speaks against food distinctions in v. 7—nonspiritual and ancient fables enslave you who give in, as if true godliness and God-pleasing piety consists in outward ceremonies like distinguishing between foods. But you train yourself in godliness which is far more beneficial and necessary than to practice such external statutes.
(Schola Pietatus-Volume 1 by Johann Gerhard, Repristination Press, p. 22)